No abstract

Magnetic and specific-heat measurements are performed in three different samples of LaMnO 3+δ , with δ = 0.11, 0.15 and 0.26, presenting important disorder effects, such as carrier localization, due to high amounts of La and Mn vacancies. For the samples with δ = 0.11 and 0.15, magnetic measurements show signatures of a two-step transition: as the temperature is lowered, the system enters a ferromagnetic phase followed by a disorder-induced cluster-glass state. Spin-wave-like contributions and an unexpected large linear term are observed in the specific heat as a function of temperature. In the sample with the highest vacancy content, δ = 0.26, the disorder is sufficient to suppress even short-range ferromagnetic order and yield a spin-glass-like state.75.40. Cx, 75.30.Ds

No abstract

No abstract

We report on low-temperature thermal expansion and specific heat measurements in a series of non-random composites YBCO/Ag x wt% (x = 0, 6, 11 and 23). A reference YBCO polycrystalline sample is also investigated. At the lowest temperatures, the expansivities and specific heat are analysed as sums of a extrinsic T -linear term and a T 3 -Debye contribution. The Gr üneisen parameters are determined and shown to be almost constant for T ≥ 60 K. The values of the Gr üneisen parameters increase with the silver content in the composites.